The invention relates to an apparatus for the provision of substantially vertical drain channels in the ground such as in grass fields, meadows etc., comprising sets of pin-shaped elements, driven by means of a rotatable shaft, journalled in the frame of the apparatus, the sets of pin-shaped elements being provided mutually adjacent in the longitudinal direction of the shaft.
Apparatus are known wherein the pin-shaped elements are provided radially on a rotor. If there is a predetermined ratio between the propagation velocity of the apparatus, which is usually mounted to a tractor, and the rotor velocity the pins penetrate substantially vertically into the soil and also leave the soil thereafter substantially vertically. The pins, however pivot through a small angle during their contact with the soil whereby at least the end of the hole made that is adjacent to the soil surface becomes somewhat slit-shaped and the wall of the hole is locally compacted or compressed. Moreover, the turf or grass surface is damaged which in many cases as for example for sports fields is not allowable. This phenomena increases in proportion to the increase in the penetration depth of the pins. The result of these features is that an insufficient amount of rain water may be stored in the soil so that the field becomes soggy with heavy rainfall. It is due to the compression of the hole wall, that water is not permitted to reach the soil below the turf and the temporary water storage space (prior to sinking downwardly into the soil, which requires some time) is sufficient due to the shallow holes.
The invention aims at removing the above mentioned disadvantages and providing an apparatus for draining sports fields etc., which results in a much larger discharge possibility for water without appreciable damage to the turf.
This is achieved according to the invention in that each pin-shaped element, including one or more pins, is pivotably connected at its end remote from its penetrating end to one end of a first rod, which is pivotably secured at its other end to the frame of the apparatus, while a second rod, extending substantially parallel to the first rod, is connected pivotably at one end to the pin-shaped element below the pivot point of the first rod and is connected likewise pivotably at its other end to the frame of the apparatus. A spring biassed section is provided in the second rod whereby the rod may increase in length when the pin or pins are loaded but resume its original length under the influence of the spring force when the load is removed.
Preferably the driving movement of the pin-shaped elements is achieved in that the end thereof is connected to a connecting rod of a crank mechanism driven by the rotary shaft. Alternatively the pin-shaped elements may be driven in different manner, e.g. through pneumatic or hydraulic piston-cylinder units actuated through valves which are switched by cams provided on the rotary shaft when this shaft is rotated. However, the preferred embodiment is cheaper.
Due to the reciprocating movement of the connecting rod or piston drive, the movement of the pins takes place substantially vertically in the driving-in direction into the soil, contrary to a tangential movement when they are rotary driven directly by the shaft. When the pins penetrate into the soil, the crank is substantially in its lower dead centre so that the pivot point of the pins does not move in any substantially tangential direction. At the moment in which the pin tends to leave the soil, the tangential velocity component increases but due to the spring biassed portion in the second rod, the pin pivots around its lower point, whereby the hole made is much enlarged at its lower end without appreciable widening of the upper end. The result is that the hole becomes larger than with the known apparatus so that it may contain much more water while the looser lower soil material is crumbled by the pivotal movement and no compressed walls are obtained so that the whole wall is porous and permits a quicker passing of the water as has been found by experiment.
In order to permit the resilient yielding of the pin-shaped elements, the second rod in a preferred embodiment comprises two parts namely a sleeve and a rod slidably inserted into the sleeve, each having an abutment. A compression spring is provided around the rod within the sleeve in engagement with the abutments.
When failure occurs of a pin, e.g. when it hits a stone in the soil or with advanced wear of a pin, it is easily replaceable according to the invention by mounting each pin of a pin-shaped element in a releasably connected block at its end remote from the penetrating end. The block carrys the pivot point of the second rod.
The invention will hereunder be further illustrated with reference to the drawing in which an example of an embodiment of the apparatus according to the invention is shown.